A conventional carving cutter is applied to carve letters, images or patterns on a metal workpiece. With reference to FIGS. 13 to 15, a carving cutter 30 is made of carbide material and contains a cutter arbor 31 and a cutting portion 32, wherein the cutting portion 32 is comprised of a flatly top surface 321 located at a first central line 320 of the cutting portion 32, a right cutting rim 322, a left cutting rim 323, and a cutting edge 324 arranged at five degrees relative to a level. FIG. 15 is an amplified view of the cutting portion 32, a distance between the first central line 320 of the cutting portion 32 and a second central line 310 of the cutter arbor 31 is an eccentric value e, and a width radius Y is defined between a distal end of the cutting edge 324 and the second central line 310, a slot width cut by the carving cutter 30 is 2Y. The carving cutter 30 is used to perform a cutting of little volume based on a designed eccentric value e, so only the right cutting rim 322 and the cutting edge 324 can be used to carve the workpiece.
The eccentric value e is selectively changed to cooperate with the width radiuses Y, wherein the eccentric value e is ranged within 0.01 to 0.06 mm and the width radius Y is ranged within 0.05 to 0.3 mm. The matching condition between the eccentric value e and the width radius Y is quite strict. In general, when e=0.01, Y=0.05; when e=0.02, Y=0.1; when e=0.03, Y=0.15; when e=0.04, Y=0.2; when e=0.05, Y=0.25; and when e=0.06, Y=0.3. Accordingly, when a mismatch between the eccentric value e and the width radiuses Y occurs, the cutting edge 34 is used in an excessively eccentric condition, thereby carving the workpiece imprecisely.
As shown in FIG. 16, when the carving cutter 30 is used in a condition of e=0.03 and Y=0.05 (i.e., the slot width=0.1 mm), due to the eccentric value e is over a set value, the cutting edge 324 is located at a right side of the second central line 310 of the cutter arbor 31, such that the left cutting rim 323 extends to the right side of the second central line 310, hence the carving cutter 30 cannot cut the workpiece smoothly, thus causing burrs or damaging the cutting edge 324. In other words, when a user desires to carve slots with various slot widths, the user has to buy multiple carving cutters 30 of which eccentric values e (or width radiuses Y) are different.
Furthermore, as illustrated in FIGS. 13 to 15, when the cutting edge 324 and the right cutting rim 322 are not sharp, they are ground by a grinding machine, but a size of the cutting edge 324 is quite small, so it cannot be ground exactly. In addition, the right cutting rim 322 and the left cutting rim 323 both have to be ground precisely, or the eccentric value e defined between the first central line 320 of the cutting portion 32 and the second central line 310 of the cutter arbor 31 changes so that the width radius Y changes as well. For instance, when the eccentric value e increases to over the set value, the cutting edge 324 is located at the right side of the second central line 310, and the left cutting rim 323 extends to the right side of the second central line 310 (as shown in FIG. 16), such that the carving cutter 30 cannot cut the workpiece smoothly, thereby causing improper cutting precision.
FIG. 17 shows a conventional disposable carving cutter 40, which contains a cutter arbor 41 and a holder 42 fixed on a distal end of the cutter arbor 41. The holder 42 has a screw orifice 421, a distance between a central position of the screw orifice 421 and a first central line 400 of the cutter arbor 41 is an eccentric value e. The screw orifice 421 of the holder 42 is provided to lock a disposable carving blade 50. The disposable carving blade 50 is in a rhombus shape and includes a right cutting rim 51 and a left cutting rim 52 between which is defined a V-shaped portion. The V-shapes portion has a cutting edge 53 formed on a distal end thereof, and the right cutting rim 51 is symmetrical to the left cutting rim 52, wherein an intersection point of distal ends of the right cutting rim 51 and the left cutting rim 52 is located at a second central line 500 of the disposable carving blade 50, and a stepped aperture 54 is defined at central position of the disposable carving blade 50, wherein the stepped aperture 54 corresponds to the screw orifice 421, and the second central line 500 passes through central positions of the screw orifice 421 and the stepped aperture 54. When the disposable carving blade 50 is locked on the holder 42, a distance between a distal end of the cutting edge 53 and the first central line 400 of the cutter arbor 41 is a width radius Y, and only the right cutting rim 51 and the cutting edge 53 can cut workpiece. After the disposable carving blade 50 is dull, it is replaced and no need to be grounded. Nevertheless, a new disposable carving blade 50 has to cooperate with a holder 42 with a fit eccentric value e so that the cutting edge 53 and the left cutting rim 52 cannot rightward move away from the first central line 400. In other words, as the eccentric value e is set on the cutter arbor 41 (i.e. is defined by the relative position between the holder 42 and the cutter arbor 41), when the user replaces the disposable carving blade 50 to adjust the width radius Y, he/she has to replace the cutter arbor 41 at the same time so as to match the eccentric value e with the width radius Y properly, thus increasing use cost.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.